Apparatus fob measuring rate of



1 M. A. TREUHAFT APPARATU FOR MEASURING RATE OF CHANGE Filed Dec. 5

as g I us W IM/VE/VTOR a4 as m rl This invention relates to the art of instrudescribed in United States Patent 1,338,358 and mentation, and more particularly to the detection others. 1

of the rates at which physical functions are In view of the shortcomings of existing appa changing. Although the invention is of broad ratus, it is a general object of my invention to application to changing physical functions in 5 provide apparatus capable of almost universal general, a specific application is described herein application to the detection of the .rate at which in which the invention is especially important. any physical function is changing, and new con- Among these are the measurement of rates of cents have resulted which make possible the rechange of temperature, conductivity and ionic 'alization of an instrument of greater sensitivity concentration. than has reviously been considered attainable.

A common method of detecting and measuring For example, I have actually constructed and rates of change is to measure the physical funcoperated apparatus in accordance with my intion at desired intervals and divide the difference vention which has successfully measured rates of the readings 'by the elapsed time between them. of temperature change as small as 0.07 degree Such a procedure is often laborious, and signifii5 ,centigrade per hour. cant changes may be overlookedunless readings It is well known that the rate at which any are taken at frequent intervals over a considerfunction, 11:4 (t) is changing is given by the first able period. Therefore an instrument for the derivative of that function with respect to time; direct indication of rates of change is highly dethus, the derivative of this function at the time sirable. t=ti is Apparatus has heretofore been suggested for the detection of rates of change. Such apparatus l hm w: hm

, .has been capable of detecting rates of change only and to a fairly good approximation,

, a vertically hanging pendulum will suffer an ancially acceptable index of the rate at which a irth United States Patent1,280,508, and in many means for delaying the eflect of that. function to o ers.

atmospheric pressure is changing becomes greatof change is to be measured so that it is long Patented Feb. 13, 1945 i i UNITED STATES PATENT OFFICE -APPARATUS FollglAgAgRmG RATE OF Milton A. Treuhaft, Weehawken, N. J assignor to John C. Batchelor Application December 5, 1940, Serial No. 368,591 4 Claims. (Cl. 73-432) has been relatively elementary and crude, and

of relatively great magnitudes and of simple functions such as accelerations of motion, rates d n.- (t Ag of aircraft climb, and the like. gi Ll, 1

. Accelerations, which are nothing more than rates of change of velocity, have frequently been Where tzti, or At is small, no appreciable error measured by simple inertia devices. For example, will result, and Ay/At'may be taken as a commergular displacement away from the vertical when function is changing.-

a horizontal acceleration is impressed 'upon it: In accordance with one form of my invention The extent of this angular displacement will be which can be made very sensitive, I providedea function of the acceleration which is imparted tecting means responsiveto the value of a physito the pendulum. A typical embodiment of an cal function which is subject to variations with accelerometer employing this principle is shown respect to time, and further provide delayin two different degrees. I then employ means for Ra s of a r r t m h al f qu ntly 4o producing aresultant physical manifestation corbeen measured by measuring the rate at which responding at any instant to the dlflerence beatmospheric pressure is changing during climbtween the contemporaneous values of the two ing flight. The space within a closed container delayed functions. having atmospheric access only through a re- A first delay is important in order to provide stricted passage will not follow changes in atmos- 4o a certain integrating period to remove the effect pheric pressure instantaneously. Accordingly, of minor variations in the physical function which when the atmospheric pressure changes, a temare not significant and which would adversely porary pressure difference will exist between the affect the usable sensitivity of the instrument. space within the container and atmospheric pres- This first delay may be selected in view of the sure, whichwill be greater as the rate at which 60 conditions surrounding the function whose rate er. Measurement of this pressure difference will enough to yield the desired integration yet short afford an indication of the rate at which the enough so that significant changes are not ironed pressure about the instrument is changing. A out.-- For'some applications, forexample. where typical embodlment of this kind of apparatus is minor variations are or small magni e: or

constant, then 'will therefore be an index ability where high sensitivity is not required. the first devlgirt may be omitted.

h two delays as just mentioned having delaying times 01' hand t1, the value of the funcand since (t2-tl) may u ually be maintained where K= (ts-ti). a

Thus. a physical manifestation corresponding to {(tz) -/(t1) will also correspond to du/dt and of the value of the rateat .whichthe function is chansins.

When my new result which are capable of detecting equilibria almost as soon as they are reached and without waiting [or an appreciable in time: of detecting incipient instabilities before they. have had an opportunity to tudes; and of detec maxima and minima oi 01 my apparatus m kes curate prognostication by de an esseninstantaneous trend without awaiting the I shall refer to the which:

'isure 1 shows or temperature change: and

Figure 2 and 3 represent two forms of apparatus suitable for the rate or change or concentration at an electrolyte.

The me surement or the may readily be accom it my invention by employing in Figure 1. I

This apparatus compl'lsesessentially a pair of the cell. In the illustrated embodiment. the first cell ll comprise a container 88 having a pair of dissimilar electrodes 04 and II and fllbd with an appropriate electrolyte II to cooperate with the electrodes to produce an electrical potential diiierence between the II, It. Die cell II is provided with a moderate amount 01' thermal insulation 8! to provide a time delay before the electrolyte It will reach the temperature or the medium in which the cell ll may be immersed;

thecell l2 comprlsesacontainer ll predetermined reach undesirable masniv apparatus for measuring a rate pen at at least ent distances from the cell 82 may be' immersed.

The cells II and ike. I1, now, after an been established; the

equilibrium condition has temperature of the medium between the terminals 94, vII so that a potential diiierence will result, between; the terminals ll. The potential sensitive instrument 8! conn'ected to the terminals 91, 98 will indicate the potential diii'erence, which will be a function of the rate at which the temperature of the medium is changing.

Some evidence or the breadth'of applications of my new concept of rate of change-determination maybe the neighborhood of one electrode'than oi the other, an electromotive between the two electrodes.

, Referring now specifically-to Figure 2, I have provided a pair of insulatinz tubes I and Ill one end, these tubes beine adaptedfor immersion in an electrolyte it! whose I II respectively, but at dinerthe respective openings"! The electrodes ill and 1N are comand i".

- posed of a metal corresponding to the ions whose rate or change oi concentration is to be measured. Conducting leads I" and I" are provided connecting the electrodes. ill minals Ill and Ill between which any potential generated by the cooperation-oi the electrodes and the electrolyte may appear. A pair of openlngs Ill and II! are provided in the tubes]... ill to prevent air locks.

An indicator H3 is provided for potential diil'erence between the terminals v.lll and I.

meable or semi-permeable membranes Ill and Ill may be placed force will be generated and ll ltiilihetel'lrelying on the different spacings from the openelectrical conductivity of a column of fluid conings I05, I to theelectrodes I03, I04. tained in the tube I'I6 between the electrodes I22, For the purpose of illustration, let us assume I23. The tube H1 is likewise provided with a pair that the solution in question contains only one of electrodes I21, I28 and likewise carried on the type of anion and one type of cation. Then, lead-in wires I30, I29 to constitute a second conwhen the ionic concentration of the electrolyte ductivity cell I3I. Construction of the instruimmediately adjacent the openings I05 and I06 ment and measurements therewith are usually increases as a result, for example, of the addition simplified by making the geometrical configuraof more solute, this increased number of ions will tion and the correlation of the electrodes in the gradually diffuse into the electrolyte contained .10 two tubes almost identical, but dissimilar strucwithin the tubes I00 andIOI, but will reach the tines may be employed when circumstances so nearer electrode I03 before reaching the farther dictate. electrode I04. In other words. two difierent time The two conductivity cells I and I3I are asdelays will be introduced in the establishment of sociated in a conjugate network with the resistors ionic equilibria at the electrodes I03 and I04, 1:, I32 and I33. This network is energized by an During the period of time when the concentraappropriate energy source I34, shown in this intion of ions adjacent the electrode I03 is greater stance as a battery connected across one pair of than that adjacent the electrode I04, a. potential conjugate terminals I35 and I35. A potential difierence'will be created between the'terminals sensitive instrument I31 is provided across the I09 and H0, and this potential difference will vary other pair of conjugate terminals I38 and I39 to as the rate at which the ionic concentration adjadetect any unbalance of the bridge circuit concent the openings I05 and I00 is changing. The stituted by this apparatus. In operation, the indicator II3 will thus measure the rate at which resistors I32, I33 are so adjusted that when the the ionic concentration is changing. After a conductivity cells I26 and I3I contain identical concentration change and complete diffusion electrolytic solutions, no potential will exist across have been effected, an equilibrium condition will the terminals I38, I33, and the instrument exist whereat thei nic concentration about each will remain undeiiected. Thus, if the cells I26 electrode is equal and hence no potential dinerand I3I are immersed in a substantially homoence will exist between the terminals I09 and geneous electrolytic solution and an equilibrium IIO. Th s, zero rate of change'will be indicated 3 condition is permitted to be reached, no deflecon the indicator II3. tion of the instrument I31 will occur. It now the It will be seen that the reverse of thismode of concentration of the fluid medium is changed, as operation will exist when the ionic concentration by' adding solute, for example, the concentration of the electrolyte adjacent the openings I05 and of the electrolyte within the cells I26 and I3I I00 is decreased as a result for example, of the will be changed by molecular diffusion, thermal addition of mor solvent. Under this circumconvection, and for other reasons. In the embodistance, ions will diffuse out of the solution then ment shown in the diagram, the concentration contained in the tub "1 a but h ionic within the cell is changed principally by circulaconcentration immediately adjacent the electrode tion, as indicated by the arrows. The cell I26, W3 will decrease more quickly than that immedi- 40 however, to which fluid access through the openately adjac nt the electrode Thus, a P ings H8 and H9 is relatively easy,. will reach a ti9-1 Opposite that generated when the iomc new equilibrium condition relatively promptly. concentration was increased W111 e generated. The cell m on the other hand, offering relativebetween the electrodes I03 and I04 and will con- 1y restricted access through th o enings I20 and Sequenfly be lmpressed upon the terminals I2I will arrive at equilibrium considerably more and H0. Accordingly, the indicator II3 will pro- Thus, a time delay will exist in the an indication in the Opposite sense from that rival of one cell at equilibrium over the other, so produced when the concentration was increased that a substantial interval will exist during which Still further, the time constant in this embodivthe bridge circuit m be l nced and a potenment will frequently be afiemd by the that tial will exist across the terminals I30 I39 to encurrent flowing in the circuit including the elecergize the instrument macs and the indicmr itself perm If new the concentration of the fluid medium cause the migration of-ions in a direction which is decreased as by adding solvent, for example assists diffusion to create an equilibrium. Proper an opposite routine Wm occur m which the com allowance can readily be made this ded centration within the cell I3I will decrease more factor however by calibration of the meter or slowly than that within the cell I25 and a deotherwise.

flection in the opposite direction on the instru- Fgure imuslmes modified form rate of ment I31 willbe caused. If, moreover, the concenconcentration change detection apparatus operatnation of the fluid me d1 um s oundmg the cells mg nductmw m z Ri :3? I26 and I3I is changing mo or less continuously, 2 3:, :32:32; e ga- :5 zi as 52 a continuous unbalance wi exist varying in magnitude in accordance with the changing concenprovided, the first tube I I6 havingrelatively wide d the magnitude t the signal appea-b o ni s H8 and H3 through which a fluid me- Fm an fi f have relatively ready access to the mg across the terminals I38, I39 and energizing inside thereof. The'tube- II1, on the otherhand. instrument Wm be a function the rate 1 tiv 1 meted o mugs no at which'the concentration is changing. g f;? 3 ;;fi;; ,;,{f, fluid f can It will be understood that in the detection of obtain onlyrelatively slow access to the space rates temperature changev my detector need within the'tube.

The tube no is provided with a pair or elecs investisatedr example, radiant energy trodes I22, I23, which may be of any 5\1ltab1e mafrom the medium may be caused to fall upon the term. such as nickel, cal-fled the 1 5, ir detector. Moreover, if the thermal output of the a conductivity cell I20 capable of measuring the 76 used to measure the rate of change of opacity or not be in physical contact with the medium be,-

I25, I24 to produce what may be considered to be medium remains constant, my detector may be specifically mentioned. Furthermore, in the l0 between the potentials generated by said cells.

shown may be devised by those skilled in the art. mutation on said first generating device having a to those skilled in the art. pedance and means for measuring e te a voltage of the series circuit comprising said first 1. Apparatus for measuring the rate of change 20 and second generating devices. of temperature of a medium which comprises 4. Apparatus for measuring the rate of change first and second electromotive iorce generatins ofaphysical function which comprisesaflrst eleccells constructed and adapted to enerate electrolytic signal-producing cell sensitive to said ing the difference between the potentials genand element witha prede time delay. and

erated by said cells to thereby measure the rate 35 measuring means for dete the instanat which the temperature or said medium is taneous diirerence between the magnitudes oi the changing. signals produced by'said first and second signal- 2. Apparatus for measuring the rate of change producing elements.

of the temperature of a medium which om rises 1mm n Arrfirst and' second electro-motive force generating 40 

